Abstract: An aberration correcting device is placed in an optical path extending from a light source of an optical pickup apparatus for irradiating a light beam onto an optical disk to the optical disk. The device includes a pair of light-transmission substrates at least one of which is held freely movable in a way that a major surface thereof moves in a direction vertical to the optical path, and which have complementary curved surfaces facing, and apart from, each other. The curved surfaces are formed in such a manner as to cause the optical path length of a light beam transmitting the pair of light-transmission substrates to be changed by movement of the light-transmission substrates, thus imparting a phase difference to a transmitting light beam, while allowing the phase difference to keep an advancing direction of the light beam thereby to minimize a comatic aberration caused by the optical disk.

Abstract: An optical pickup is provided for recording and reproduction of information onto and from an optical disk. In the optical disk, in a forward optical path, a single polarized optical beam is converted to plural polarized optical beams. Polarization modes of the plural polarized optical beams are then converted to a polarization mode suitable for one of the recording and the reproduction to produce polarization-converted optical beams and to radiate the polarization-converted optical beams to the disk. In the backward optical path, polarization modes of the polarization-converted optical beams reflected from the disk are returned to the same polarization mode as that of the plural polarized optical beams, so that plural polarized reflected optical beams are produced. Polarization modes of the plural polarized reflected optical beams are then returned to the same polarization mode as the single polarized optical mode.

Abstract: A spherical aberration correcting unit corrects an aberration caused in an optical beam radiated toward an information recording medium and focused on the medium. The correcting unit comprises an aberration corrector, driver, light receiver, and controller. The aberration corrector, which is composed of a plurality of optical members, forms the optical beam into a parallel pencil and corrects the aberration caused in the optical beam. The driver drives any one of the optical members in an optical axis direction of the optical beam. The light receiver receives light reflected from the medium to produce a light-reception signal from the received light, and the controller controls the driver based on the produced light-reception signal.

Abstract: The collision preventing device is used for an optical pickup device for recording or reproducing information to or from an optical information recording medium. The collision preventing device has a shock absorbing layer to prevent a contact of an objective lens and a surface of the recording medium. The shock absorbing layer is laminated on the portion extending from the circumferential edge of the effective-diameter area of the objective lens to the outside edge or to the outside of the objective lens and has a thickness in such a manner that the shock absorbing layer comes in contact with the surface of the recording medium prior to the effective-diameter area, when the objective lens comes close to the surface of the recording medium.

Abstract: The present invention relates to an optical multi-layer information recording medium for recording information therein and/or retrieving information therefrom upon radiation of a convergent beam of light. The recording medium includes at least two pairs of recording layer and light-transmissive layer stacked one after another. A first recording layer proximal to a beam radiation side and a second recording layer distal from the beam radiation side are made from a material that satisfies a function including the following parameters; transmissivity and absorptance of the first recording layer, absorptance of the second recording layer, a numerical aperture on the first recording layer, a numerical aperture of the second recording layer, and transmissivity of between the first and second recording layers. Even if the numerical apertures change with spherical aberration compensation made to respective recording layers, a power density of a light spot does not change.

Abstract: The present invention relates to an optical pickup having a constant numerical aperture even if spherical aberration is compensated for. The optical pickup is used in an information recording and/or reproducing machine. The information recording and/or reproducing machine records and/or reproduces information in a recording medium upon radiation of a light beam from a light source. The optical pickup includes a condensing optical system for condensing the light beam from the light source onto a recording layer of the recording medium. The condensing optical system includes an object lens. The condensing optical system also includes an aperture positioned about a focal length of the object lens apart from a position of a principal incidence plane of the object lens toward the light source along an optical axis of the condensing optical system.

Abstract: An information recording at a high density to an information recording medium and a proper reproduction of information which has been recorded on the information recording medium at a high density are realized. Optical characteristics of an information recording medium are measured and information regarding the measured optical characteristics is previously recorded in a proper area on the information recording medium. When an information recording system records information to the information recording medium on which the information regarding the optical characteristics has been recorded, the information regarding the optical characteristics is read and a proper information recording state is adjusted on the basis of the information regarding the optical characteristics, thereby allowing the information recording to be performed.

Abstract: A lens made of at least one of a resin and glass includes a lens effective diameter area, a peripheral area formed integral with the lens effective diameter area and located at a periphery of the lens effective diameter area, and at least one marker area located in the peripheral area and formed on a circle whose center is a center of the lens effective diameter area.

Abstract: A polarization hologram lens includes: a first portion, positioned at a center of the hologram lens, on which no grating pattern is formed; and a second portion, positioned at an outer circumferential area of the first portion, on which grating patterns are formed, wherein the grating patterns do not diffract a light beam of a first polarization direction, and wherein the grating patterns diffract a light beam of a second polarization direction perpendicular to the first polarization direction to produce a diverging diffracted light or a converging diffracted light.

Abstract: A pickup drive apparatus for recording or reproducing with respect to a recording medium such as a CD and a DVD. In the apparatus, return light produced by irradiating an optical spot is detected by a photodetector, and a push-pull signal is produced from this detection output. A tracking error signal is produced from the push-pull signal by a low-pass filter and a phase compensating circuit. A quasi-ON/OFF control signal having information of an irradiation position of the optical spot is produced from the push-pull signal by a high-pass filter, a comparator, and a single pulse generator. When the quasi-ON/OFF control signal is produced which indicates that the optical spot is positioned on a groove, the tracking error signal is outputted via switching circuits in synchronism with this signal production. A pickup is servo-controlled based on this output signal.

Abstract: An optical pickup apparatus having an irradiation optical system for condensing a light beam on a track of a recording plane and a photodetection optical system for guiding return light to a photodetector to detect a focal error includes a holographic lens provided in the optical path of the return light for outputting 0-th and ±1st order diffracted lights based on the return light; an optical element provided in front of or behind the holographic lens for providing astigmatism; photodetectors for receiving the 0-th and ±1st order diffracted lights; and servo-signal generating operation circuits connected to the photodetectors for generating a first and second focus error signals having a first and second capture ranges based on the output signal of the photodetector.

Abstract: The collision preventing device is used for an optical pickup device for recording or reproducing information to or from an optical information recording medium. The collision preventing device has a shock absorbing layer to prevent a contact of an objective lens and a surface of the recording medium. The shock absorbing layer is laminated on the portion extending from the circumferential edge of the effective-diameter area of the objective lens to the outside edge or to the outside of the objective lens and has a thickness in such a manner that the shock absorbing layer comes in contact with the surface of the recording medium prior to the effective-diameter area, when the objective lens comes close to the surface of the recording medium.

Abstract: The present invention relates to an optical pickup having a constant numerical aperture even if spherical aberration is compensated for. The optical pickup is used in an information recording and/or reproducing machine. The information recording and/or reproducing machine records and/or reproduces information in a recording medium upon radiation of a light beam from a light source. The optical pickup includes a condensing optical system for condensing the light beam from the light source onto a recording layer of the recording medium. The condensing optical system includes an object lens. The condensing optical system also includes an aperture positioned about a focal length of the object lens apart from a position of a principal incidence plane of the object lens toward the light source along an optical axis of the condensing optical system.

Abstract: The present invention relates to an optical multi-layer information recording medium for recording information therein and/or retrieving information therefrom upon radiation of a convergent beam of light. The recording medium includes at least two pairs of recording layer and light-transmissive layer stacked one after another. A first recording layer proximal to a beam radiation side and a second recording layer distal from the beam radiation side are made from a material that satisfies a function including the following parameters; transmissivity and absorptance of the first recording layer, absorptance of the second recording layer, a numerical aperture on the first recording layer, a numerical aperture of the second recording layer, and transmissivity of between the first and second recording layers. Even if the numerical apertures change with spherical aberration compensation made to respective recording layers, a power density of a light spot does not change.

Abstract: An optical pickup includes a light source for emitting more than two light beams whose wavelengths are different from each other, and an objective lens including a first lens and a second lens. The first lens is a lens for collecting each light beam onto a recording medium. The second lens is a lens for compensating chromatic aberration in the light beams. The second lens is placed on the first lens in contact and is located across the optical path of each light beam. The absolute value of the difference between the Abbe number of the first lens and the Abbe number of the second lens is greater than 10.

Abstract: The disclosure is a molded glass objective lens. The objective lens includes a first surface having a center symmetric convex surface shape at least in a range of an optical beam passing therethrough, a second surface having a center symmetric effective surface shape at least in a range of an optical beam passing therethrough on the opposite side opposing to the first surface, and a center symmetric cylindrical side surface crossing with the first surface. A center curvature radius of the first surface is defined in a particular range led by the volume of the molded glass objective lens and the volume of a virtual lens portion surrounded by a cylindrical surface including the first and second surfaces and the cylindrical side surface.

Abstract: A lens made of at least one of a resin and glass includes a lens effective diameter area, a peripheral area formed integral with the lens effective diameter area and located at a periphery of the lens effective diameter area, and at least one marker area located in the peripheral area and formed on a circle whose center is a center of the lens effective diameter area.

Abstract: A complex objective lens includes a first optical element having a first surface including a convex aspherical surface shape and an opposite side surface opposing to the first surface; and a second optical element having an exit surface through which an optical beam passing and an entry surface opposing to the exit surface. The opposite side surface opposing to the first surface of the first optical element and the entry surface opposing to the exit surface of the second optical element are directly contacted to each other.

Abstract: A pickup device for writing or reading information onto or from an optical disk having a recording surface that is covered with a transmission substrate.

Abstract: A light source is provided for emitting a light beam. The light beam from the light source is applied to a recording and reproducing plane of an optical disc and to a front surface of a transparent substrate of the optical disc. A photodetector is provided for detecting return light beams from the recording and reproducing plane and the front surface. A first signal is generated based on an output signal of the photodetector dependent on the return light beam from the recording and reproducing plane, and a second signal is generated based on an output signal of the photodetector dependent on the return light beam from the front surface. A signal relating to thickness information on a thickness of the transparent substrate is produced by comparing the first and second signals with each other.